Heat-sensitive recording materials of the kind which utilize electron-donating colorless dye precursors (hereinafter referred to as color formers) and electron-accepting compounds (hereinafter referred to as color developers) are disclosed, e.g., in Japanese Patent Publication Nos. 14039/70 (corresponding to U.S. Pat. No. 3,539,375) and 4160/68. Heat-sensitive recording materials (reference is also made herein to recording papers, as a typical heat-sensitive recording material) of these kinds have advantages in that they ensure noiseless recording due to non-impaction in recording action, and further, they do not require toner, ink ribbon, and other consumable materials except recording paper, so maintenance of such consumable materials becomes needless. Due to these advantages, such heat-sensitive recording materials have many uses, for example, facsimile equipment, printers, and so on.
These heat-sensitive recording materials have so far been required to have the properties of providing records with sufficient color density, having sufficient sensitivity to character-printing, having a high degree of whiteness in the background, and making formed color fast. Up to the present, they have continued to undergo improvements in these properties. In addition to the foregoing properties, good slippability has recently become a significant required of the recording layer.
This is because it has come to be improper with the speeding-up of recording to disregard the friction that occurs as a result between a heat-sensitive recording material and a thermal head of a heat-sensitive recording apparatus and the frictions caused by bringing a heatsensitive recording material into contact with other various parts of a recording apparatus.
Since a great force is needed for transport of the recording paper when the above-described frictions are great, it occurs upon printing operation that a paper-sending roll suffers from an insufficiency of torque, resulting in contraction of printed characters, or, what is worse, cessation of paper transport. These phenomena tend to occur pronouncedly under high temperature and high humidity conditions, and the readiness to cause these phenomena increases approximately in proportion to a co-efficient of statistical friction between a heat-sensitive recording layer and a thermal head surface (made of a vitrious material), and to those between the heat-sensitive recording layer and various parts of a recording apparatus (made of metals, resins, and so on). Accordingly, it has now become indispensable for high-speed recording to heighten the slippability of a heat-sensitive recording layer on a thermal head and so on.